This invention relates to pressure release devices, assemblies, and components, as well as methods of forming the same.
Many types of pressure release devices exist in the art. These pressure release devices may include, for example, explosion panels, rupture disks, vacuum breakers, tank vents, and valves. An explosion panel is one type of pressure release device that is typically used to provide an emergency pressure release under deflagration conditions in an environment such as, for example, a silo or a dust collector. An explosion panel may be subject to both a positive pressure differential or a negative pressure differential. In a positive pressure differential, the pressure within the environment is greater than the external pressure. In a negative pressure differential, the external pressure is greater than the pressure within the environment. It is typically desirable for the explosion panel to open when exposed to a predetermined positive pressure differential and to withstand a negative pressure differential, as well as normal service conditions that may produce fluctuations between both negative and positive pressure differentials.
Various methods may be used to control the predetermined positive pressure differential at which the explosion panel will open. For example, a series of slits may be cut into the explosion panel to define a series of “tabs.” The slits may be cut into the opening section of the explosion panel or the flange section of the explosion panel or both. An explosion vent may be substantially flat in shape or may have a domed opening section with a flat perimeter flange area. These tabs are configured to fail in tension when the explosion panel experiences the predetermined positive activation pressure differential. The number and size of the tabs will control the pressure differential at which the explosion panel will open. Accordingly, the slits must be carefully cut to ensure that the resulting tab has the appropriate size.
One problem that has long been associated with pressure relief devices such as explosion panels is premature activation of the panels due to pressure fluctuations within the system being protected, vibrations caused by the equipment environment or structure to be protected, and other turbulences. Specifically, pressure fluctuations, vibration from the equipment, or other turbulences may cause the explosion panel to flex back and forth, resulting in fatigue stress to be transmitted along the unbroken portion of the panel, the tab, and at the ends of the slits cut into the explosion panel. This is particularly prevalent when the slits comprise elongated slots that are separated by relatively narrow tabs that flex repeatedly until the material comprising the tabs reaches its fatigue limit and breaks. As a result, the explosion panel may open at a pressure substantially below the desired burst pressure, enabling materials within the structure or the equipment to accidentally escape to the atmosphere, often without the knowledge of the operator. For example, pressure fluctuations in, and vibrations emanating from, equipment associated with hot air handling systems often cause such severe stress on the explosion panels that the panels prematurely fracture shortly after installation.
Various efforts have been made to improve the fatigue resistance of explosion panels. For example, U.S. Pat. No. 4,663,126 describes an explosion panel assembly including two explosion panels disposed in spaced, face-to-face relationship along with a core of expanded polyurethane foam interposed between the panels which purportedly functions to dampen vibrations received from the structure and transmitted to the explosion panels. The foam is introduced in an initially flowable condition into the space between the panels and thereafter expands while curing to a solidified configuration for continuously exerting pressure on both of the panels. The foam material, when cured, strengthens the assembly by providing support to the central portions of the explosion panels. As the foam cures, however, it rigidly adheres to the surfaces of the explosion panels, thereby forming a substantially solid laminated structure, which undesirably increases the strength of the explosion panels. As a result, explosion panels having a low burst pressure are more difficult to achieve. In addition, if this structure is used in a high temperature environment, and because many foams begin to degrade at a temperature of about 220° F., the foam will shrink and break down, thereby reducing the fatigue resistance of the explosion panel and impairing the sealing properties of the pressure relief device.
There is a need in the industry for an explosion panel that is capable of withstanding fatigue, and which can operate in a high temperature environment and provide low burst pressures.